(grā′ting) noun
1. A grate.
2. Physics An optical device for the dispersion of light waves and the production of spectra, usually consisting of a series of very fine parallel grooves cut in the surface of polished metal or glass, sometimes of a suitably mounted crystal: also called diffraction grating.

(grā′ting) adjective
Harsh in sound; rasping; irritating.
—noun The act or sound of rasping.
—grat′ing·ly adverb